The present invention relates to an optical element having an antireflection film. It relates to an optical element having an antireflection film that has excellent adhesiveness between a plastic substrate and the antireflection film, abrasion resistance, heat resistance, alkali resistance and impact resistance.
Heretofore known are optical elements having an antireflection film provided on a plastic substrate. Also known are optical elements having a thin metal film layer provided on the surface of a plastic substrate for enhancing the adhesiveness between the plastic substrate and the antireflection film. For example, Japanese Patent Laid-Open No.186202/1987 discloses an antireflection film for an optical element having a thin metal film layer provided on the surface of a plastic substrate, in which the metal layer is made of a metal selected from the group consisting of copper (Cu), aluminum (Al), nickel (Ni), gold (Au), chromium (Cr), palladium (Pd) and tin (Sn).
However, these optical elements having an antireflection film are unsatisfactory with respect to their heat resistance and impact resistance. Therefore, it is desirable to provide optical elements having an antireflection film that have improved physical properties such as heat resistance, abrasion resistance, alkali resistance and impact resistance.
Heretofore, in general, a basic layer made of SiO2 has been provided in a plastic lens for enhancing the strength of coating films. However, the basic layer made of SiO2 has a drawback of lowering the heat resistance of the plastic lens.
The present invention provides an optical element having an antireflection film having excellent adhesiveness between a plastic substrate and the antireflection film, heat resistance, abrasion resistance, alkali resistance and impact resistance.
The present invention addresses the problems noted above. The inventors have determined that when a layer made of niobium (Nb) is provided between a plastic substrate and an antireflection film to form an optical element, the adhesiveness between the plastic substrate and the antireflection film, the heat resistance, abrasive resistance, alkali resistance and the impact resistance of the optical element are improved.
The optical element of the invention has a basic layer made of Nb, and therefore, has not only excellent adhesiveness between the plastic substrate and the antireflection film, heat resistance and impact resistance, but also excellent alkali and abrasion resistance and properties such that an absorbance index inherent to metals is low.
The basic layer may consist of Nb (that is 100% by weight of Nb), or may comprise a mixture of niobium and up to 50% by weight, preferably 25% by weight of other elements such as aluminum(Al), chromium(Cr), tantalum(Ta) and mixtures of two or more thereof. The antireflection film may also be comprised of multi-layers, and at least one of the layers is obtainable by an ion-assisted process. The basic layer comprising Nb may also be formed by an ion-assisted process.
The xe2x80x9cion-assisted processxe2x80x9d referred to herein is a well known process also called xe2x80x9cion beam assisted vapor deposition processxe2x80x9d. According to this process, a material is deposited on a substrate, such as a lens substrate, by vapor deposition using an ion plasma in a gas atmosphere, such as argon (Ar) and/or oxygen. In a common apparatus suitable to perform this process, preferred vapor deposition conditions are an accelerating voltage of 100-250V, and an accelerating current of 50-150 mA. A detailed description is given in e.g. U.S. Pat. No. 5,268,781. Further details can be derived from M. Fliedner et al., Society of Vacuum Coaters, Albuquerque, N.M., USA. p237-241, 1995 as well as from the references cited therein.
In the ion-assisted process, argon (Ar) maybe used as the ionizing gas for preventing oxidation of films being formed. Although argon is preferred, other ionizing gases such as oxygen and nitrogen, or mixtures of these gases could also be used. This stabilizes the quality of the films formed and enables easy control of the thickness of the films by the use of an optical film thickness meter.
For ensuring good adhesiveness between the plastic substrate and the basic layer and for ensuring good uniformity of the initial film morphology in vapor deposition in the ion-assisted process, the plastic substrate may be subjected to ion gun pretreatment before the basic layer is formed thereon. The ionizing gas in the ion gun pretreatment may be any of oxygen, nitrogen, Ar, or mixtures thereof. For the preferred power range, the accelerating voltage is from 50 V to 200 V, and the accelerating current is from 50 mA to 150 mA. If the accelerating voltage is lower than 50 V, or the accelerating current is lower than 50 mA, an effect for improving the adhesiveness between the plastic substrate and the basic layer formed thereon may not be sufficient. However, if the accelerating voltage exceeds 200 V, or the accelerating current exceeds 150 mA, the plastic substrate and also the cured film and the hard coat layer thereon may possibly be yellowed, or the abrasion resistance of the optical element may possibly be lowered.
In the invention, after the basic layer comprising Nb has been formed on the substrate, an antireflection layer is formed by any suitable process. For example, it may be formed by vapor deposition, such as chemical vapor deposition (CVD) or physical vapor deposition (PVD), or by other methods such as ion plating vapor deposition.
In one embodiment, the antireflection film has at least one SiO2 layer as a low-refraction layer and at least one TiO2 layer as a high-refraction layer. If desired, the antireflection film may have a metal layer comprising Nb.
For relieving the stress within the low-refraction layer such as an SiO2 layer, when the SiO2 layer is formed in an ion-assisted process in which Ar is used for the ionizing gas for SiO2 deposition, the abrasion resistance can be improved. Regarding the ion-assisting condition for obtaining the result, the ion current density on the dome in the vapor deposition device is from 15 to 35 xcexcA, and the accelerating voltage is from 400 to 700 V. If the ion current density is lower than 15 xcexcA or the accelerating voltage is lower than 400 V, both an effect for relieving the stress and an effect for improving the abrasion resistance may be hardly obtained. If, however, the ion current density exceeds 35 xcexcA or the accelerating voltage exceeds 700 V, the plastic substrate may possibly be yellowed, or the optical performance may possibly be adversely affected.
The high-refraction layer such as a TiO2 layer may also be formed in an ion-assisted process. For the ionizing gas in the ion-assisted process for forming the high-refraction layer, a mixed gas of O2 and Ar is used. The mixing ratio of O2 to Ar based on the volume of flowing gases preferably ranges from 1:0.5-2. It is possible to improve the refractive index of the high-refraction layer formed and to promote the improvement of the abrasion resistance by using an ion-assisted process. Materials for forming the high-refraction layer are TiO2, Nb2O5, Ta2O5, ZrO2, Y2O3, and mixtures thereof. Preferred examples include TiO2, Nb2O5, Ta2O5 and mixtures thereof.
As a suitable ion-assisting condition for using TiO2, Nb2O5 or their mixtures as the metal oxide, the ion current density on the dome in the vapor deposition device is from 8 to 15 xcexcA, and the accelerating voltage is from 300 to 700 V. The volume ratio of O2 to Ar in the ionizing gas mixture is from 1/0.7 to 1/1.0. If the ion current density, the accelerating voltage and the ionizing gas ratio overstep the defined ranges, the intended refractive index may not be obtained, and, in addition, its absorbance index may likely increase, and its abrasion resistance may possibly be lowered.
As a suitable ion-assisting condition for using Ta2O5or its mixtures as the metal oxide, the ion current density on the dome in the vapor deposition device is from 12 to 20 xcexcA, and the accelerating voltage is from 400 to 700 V. The volume ratio of O2 to Ar in the ionizing gas mixture is from 1/0.5 to 1/2.0. If the ion current density, the accelerating voltage and the ionizing gas ratio overstep the defined ranges, the intended refractive index may not be obtained, and, in addition, its absorbance index may likely increase, and its abrasion resistance may possibly be lowered.
A suitable thickness of the basic layer of the optical element of the invention is from 1.0 to 5.0 nm. If its thickness oversteps the defined range, the basic layer may possibly present a problem of absorbance within the film.
One embodiment of the layer constitution of the basic layer and the antireflection film formed on the plastic substrate is described below. Herein, the laminate of the 1st to 7th layers serves as the antireflection film.
Basic layer: Nb layer (film thickness: 1 to 5 nm)
1st layer: SiO2 layer (film thickness: 5 to 50 nm)
2nd layer: TiO2 layer (film thickness: 1 to 15 nm)
3rd layer: SiO2 layer (film thickness: 20 to 360 nm)
4th layer: TiO2 layer (film thickness: 5 to 55 nm)
5th layer: SiO2 layer (film thickness: 5 to 50 nm)
6th layer: TiO2 layer (film thickness: 5 to 130 nm)
7th layer: SiO2 layer (film thickness: 70 to 100 nm)
The ranges of the film thickness mentioned above are the most preferred ones for the adhesiveness between the plastic substrate and the antireflection film and for the heat resistance and impact resistance of the optical element.
Another embodiment of the layer constitution of the basic layer and the antireflection film is mentioned below. Herein, the laminate of the 1st to 7th layers serves as the antireflection film.
Basic layer: Nb layer (film thickness: 1 to 5 nm)
1st layer: SiO2 layer (film thickness: 20 to 100 nm)
2nd layer: Nb layer (film thickness: 1 to 5 nm)
3rd layer: SiO2 layer (film thickness: 20 to 100 nm)
4th layer: TiO2 layer (film thickness: 5 to 55 nm)
5th layer: SiO2 layer (film thickness: 5 to 50 nm)
6th layer: TiO2 layer (film thickness: 5 to 130 nm)
7th layer: SiO2 layer (film thickness: 70 to 100 nm)
The ranges of the film thickness mentioned above are the most preferred ones for the adhesiveness between the plastic substrate and the antireflection film and for the heat resistance and impact resistance of the optical element.
The material for the plastic substrate for use in the invention is not specifically limited. Suitable materials include, for example, methyl methacrylate homopolymers, copolymers of methyl methacrylate and one or more other monomers such as diethylene glycol bisallyl carbonate or benzyl methacrylate, diethylene glycol bisallyl carbonate homopolymers, copolymers of diethylene glycol bisallyl carbonate and one or more other monomers such as methyl methacrylate and benzyl methacrylate, sulfur-containing copolymers, halogen copolymers, polycarbonates, polystyrenes, polyvinyl chlorides, unsaturated polyesters, polyethylene terephthalates, polyurethanes, and polythiourethanes. Preferred examples include polythiourethane, diethylene glycol bisallyl carbonate homopolymers, and sulfur-containing copolymers.
If desired, the optical element of the invention may have a cured film between the plastic substrate and the basic layer.
For the cured film, in general, a coating composition is used that comprises metal oxide colloid particles and one or more organosilicon compounds represented by the following general formula (1):
(R1)a(R2)bSi(OR3)4xe2x88x92(a+b)xe2x80x83xe2x80x83(1)
wherein R1 and R2 each independently represents an organic group selected from an C1-8 alkyl group, an C2-8 alkenyl group, an aryl group, a phenyl group, a 5- or 6-membered heteroaryl group having at least one heteroatom selected from sulfur and nitrogen which may optionally be substituted by one or more C1-3 alkyl group(s), an C1-8 acyl group, a halogen atom, a glycidoxy group, an epoxy group, an amino group, a phenyl group, a mercapto group, a methacryloxy group, and a cyano group; R3 represents an organic group selected from an alkyl group having from 1 to 8 carbon atoms, an C1-8 acyl group, and a phenyl group; and a and b each independently indicates an integer of 0 or 1. For applying the coating composition onto the surface of a plastic lens substrate, any ordinary method of dip coating, spin coating, or spraying may be employed. In view of the smoothness of the coated film, especially preferred is dip coating or spin coating. Having been applied to lens substrates, the composition is cured by drying it in hot air or by exposing it to active energy rays. Preferably, it is cured in hot air at 70 to 200xc2x0 C., and more preferably at 90 to 150xc2x0 C. For the active energy rays, preferred are far-infrared rays as not damaging the film by heat.
The metal oxide colloid particles generally are fine metal oxide particles having a particle size of 1-500 nm. Preferred examples thereof are colloid particles of tungsten oxide (WO3), zinc oxide (ZnO), silicon oxide (SiO2), aluminum oxide (Al2O3), titanium oxide (TiO2), zirconium oxide (ZrO2), tin oxide (SnO2), berylliumoxide (BeO) or antimonyoxide (Sb2O5) These metal oxides may be used either singly or in admixture of two or more thereof.
The organosilicon compound of the general formula (1) includes, for example, methyl silicate, ethyl silicate, n-propyl silicate, isopropyl silicate, n-butyl silicate, sec-butyl silicate, tert-butyl silicate, tetraacetoxysilane, methyltrimethoxysilane, methyltriethoxysilane, methyltripropoxysilane, methyltriacetoxysilane, methyltributoxysilane, methyltripropoxysilane, methyltriamyloxysilane, methyltriphenoxysilane, methyltribenzyloxysilane, methyltriphenethyloxysilane, glycidoxymethyltrimethoxysilane, glycidoxymethyltriethoxysilane, xcex1-glycidoxyethyltriethoxysilane, xcex2-glycidoxyethyltrimethoxysilane, xcex2-glycidoxyethyltriethoxysilane, xcex1-glycidoxypropyltrimethoxysilane, xcex1-glycidoxypropyltriethoxysilane, xcex2-glycidoxypropyltrimethoxysilane, xcex2-glycidoxypropyltriethoxysilane, xcex3-glycidoxypropyltrimethoxysilane, xcex3-glycidoxypropyltriethoxysilane, xcex3-glycidoxypropyltripropoxysilane, xcex3-glycidoxypropyltributoxysilane, xcex3-glycidoxypropyltriphenoxysilane, xcex1-glycidoxybutyltrimethoxysilane, xcex1-glycidoxybutyltriethoxysilane, xcex2-glycidoxybutyltrimethoxysilane, xcex2-glycidoxybutyltriethoxysilane, xcex3-glycidoxybutyltrimethoxysialne, xcex3-glycidoxybutyltriethoxysilane, xcex4-glycidoxybutyltrimethoxysilane, xcex4-glycidoxybutyltriethoxysilane, (3,4-epoxycyclohexyl)methyltrimethoxysilane, (3,4-epoxycyclohexyl)methyltriethoxysilane, xcex2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, xcex2-(3,4-epoxycyclohexyl)ethyltriethoxysilane, xcex2-(3,4-epoxycyclohexyl)ethyltripropoxysilane, xcex2-(3,4-epoxycyclohexyl)ethyltributoxysilane, xcex2-(3,4-epoxycyclohexyl)ethyltriphenoxysilane, xcex3-(3,4-epoxycyclohexyl)propyltrimethoxysilane, xcex3-(3,4-epoxycyclohexyl)propyltriethoxysilane, xcex4-(3,4-epoxycyclohexyl)butyltrimethoxysilane, xcex4-(3,4-epoxycyclohexyl)butyltriethoxysilane, glycidoxymethylmethyldimethoxysilane, glycidoxymethylmethyldiethoxysilane, xcex1-glycidoxyethylmethyldimethoxysilane, xcex1-glycidoxyethylmethyldiethoxysilane, xcex2-glycidoxyethylmethyldimethoxysilane, xcex2-glycidoxyethylmethyldiethoxysilane, xcex1-glycidoxypropylmethyldimethoxysilane, xcex1-glycidoxypropylmethyldiethoxysilane, xcex2-glycidoxypropylmethyldimethoxysilane, xcex2-glycidoxypropylmethyldiethoxysilane, xcex3-glycidoxypropylmethyldimethoxysilane, xcex3-glycidoxypropylmethyldiethoxysilane, xcex3-glycidoxypropylmethyldipropoxysilane, xcex3-glycidoxypropylmethyldibutoxysilane, xcex3-glycidoxypropylmethyldiphenoxysilane, xcex3-glycidoxypropylethyldimethoxysilane, xcex3-glycidoxypropylethyldiethoxysilane, xcex3-glycidoxypropylvinyldimethoxysilane, xcex3-glycidoxypropylvinyldiethoxysilane, xcex3-glycidoxypropylphenyldimethoxysilane, xcex3-glycidoxypropylphenyldiethoxysilane, ethyltrimethoxysilane, ethyltriethoxysilane, vinyltrimethoxysilane, vinyltriacetoxysilane, vinyltrimethoxyethoxysilane, phenyltrimethoxysilane, phenyltriethoxysilane, phenyltriacetoxysilane, xcex3-chloropropyltrimethoxysilane, xcex3-chloropropyltriethoxysilane, xcex3-chloropropyltriacetoxysilane, 3,3,3-trifluoropropyltrimethoxysilane, xcex3-methacryloxypropyltrimethoxysilane, xcex3-mercaptopropyltrimethoxysilane, xcex3-mercaptopropyltriethoxysilane, xcex2-cyanoethyltriethoxysilane, chloromethyltrimethoxysilane, chloromethyltriethoxysilane, N-(xcex2-aminoethyl)-xcex3-aminopropyltrimethoxysilane, N-(xcex2-aminoethyl)-xcex3-aminopropylmethyldimethoxysilane, xcex3-aminopropylmethyldimethoxysilane, N-(xcex2-aminoethyl)-xcex3-aminopropyltriethoxysilane, N-(xcex2-aminoethyl)-xcex3-aminopropylmethyldiethoxysilane, dimethyldimethoxysilane, phenylmethyldimethoxysilane, dimethyldiethoxysilane, phenylmethyldiethoxysilane, xcex3-chloropropylmethyldimethoxysilane, xcex3-chloropropylmethyldimethoxysilane, dimethyldiacetoxysilane, xcex3-methacryloxypropylmethyldimethoxysilane, xcex3-methacryloxypropylmethyldiethoxysilane, xcex3-mercaptopropylmethyldimethoxysilane, xcex3-mercaptopropylmethyldiethoxysilane, methylvinyldimethoxysilane, and methylvinyldiethoxysilane.